Grade Level: 4th - 8th; Type: Food Science
The goal of this experiment is to learn about starches in food and demonstrate how manipulation of these starches affects the taste of food. Students remove starches by soaking potatoes, and learn how this affects the quality of food.
- How do starches affect the taste of oven-fried potatoes? What happens if this starch is removed?
- What are the major nutritional constituents in potatoes?
- How does the concentration of starch in a potato relate to the “mealiness” or waxiness of the potato?
Whether it’s the straight-chain amylase chains or branched amylopectin chains, potatoes are largely made from starch. This starch plays an important role in the cooking process. As food scientist Harold McGee explains, modern deep fryers often operate at two temperatures. Starches leak out during a first low-temperature frying and form a gluey layer on the surface of the potato. Browning takes place during a second high-temperature frying, which develops the taste and crispness of the potato. Something similar takes place when sliced potatoes are soaked in water. In addition to drawing out potassium, soaking also draws out starches – doing something similar to the first low-temperature fry. Coating the potato in cooking oil and baking it has the effect of crisping the surface starch, just like the second high-temperature fry.
- Materials are readily available in the home and grocery stores.
- Two pounds of potatoes
- Olive oil
- Basting brush for applying olive oil
- Access to a sink and stove
- Basin for soaking potatoes
- Kitchen knife
- Using a kitchen knife and cutting board, cut two medium potatoes in half length-wise. Cut these two halves length wise again. Cut each of these four pieces in half lengthwise again so that you have eight pieces that are more or less the same size. If you are using a larger potato, consider cutting each piece in half one more time.
- Divide your potato pieces into two separate batches. Cut a small notch into each potato in the first batch. The point of this notch is so you can tell these potatoes apart from the un-notched ones after the potatoes are baked.
- Line a cookie sheet with aluminum foil and lay out the un-notched potato pieces to dry.
- Fill a basin with water. Put your notched potatoes in the water and soak undisturbed for one hour. Do not disturb the potatoes; the point is to draw the starch out, not to knock the starch off.
- After they are done soaking, drain the notched potatoes. Mix them with the un-notched potatoes on the baking sheet and let dry.
- Brush all of the potatoes lightly with olive oil. Sprinkle with salt. Bake at 450 degrees for ten minutes. Using a potholder, remove the cooking sheet from the oven, and turn the potatoes. Sprinkle with more salt. Continue baking for ten more minutes.
- Remove the potatoes and let them cool until you can comfortably handle them.
- Rate the potatoes on their crispiness by bending each potato and seeing if it is crispy enough to break in two. Count the number of notched potatoes that snapped in half and the number that merely bent in two. Do the same with the un-notched potatoes. Does pre-treating the potatoes by soaking make the potatoes crispier?
Terms/Concepts:Starch, Amylose, Amylopectin, Single-frying vs. double-frying, Mealy vs. waxy potatoes
McGee, Harold. On Food and Cooking: The Science and Lord of the Kitchen. CollierBooks (1984)
Chemistry Explained: Starch http://www.chemistryexplained.com/St-Te/Starch.html